The present invention relates to an image reader to obtain image data for an electrophotographic image forming apparatus, for example, and an image forming apparatus having the image reader.
An image reader converts the reflected light obtained by illuminating a reading object such as a sheet-like document, book and three-dimensional object, by an image reading sensor such as a CCD sensor, and outputs the image data.
In many cases, in an image reader, a reflected light from a reading object is transmitted to a CCD sensor (illuminated by a illumination unit), by moving an optics including a illumination unit and mirrors along a glass plate, while remaining a reading object standstill at a predetermined position in a document holding unit (a transparent glass plate). An illumination unit is made to be able to illuminate the reading width that is a total length of an optional one side (width) of a transparent glass plate. Mirrors are given the length capable of reflecting the reflected light from the reading object illuminated over the reading width, in a predetermined direction over all areas in the reading width.
By moving the optics at a predetermined speed all along the reading length that is the total length of another side (length) orthogonal to the reading width, the reflected lights from all areas of the reading object are transmitted to the CCD sensor. The optics is moved substantially parallel to the glass plate with a predetermined space held between the glass plate. The reflected light from the reading object is transmitted to the CCD sensor through an optical element such as a lens.
Recently, it has been increased to incorporate a line CCD sensor for monochrome images for reading monochrome images at a high speed, in addition to a 3-line CCD sensor for reading color images for exactly reproducing colors.
However, the CCD sensors for color image and monochrome image are different in the spectral sensitivity and wavelength, and choice of illumination lamps is difficult. A lamp common to both color image and monochrome image is available, but the optical condition is not optimum for the two CCD sensors, and the read image quality may be deteriorated.
Thus, it has been proposed to provide two light sources for illuminating color image and monochrome image, and turn on the two light sources simultaneously when reading a color image (Jpn. Pat. Appln. KOKAI Publication No. 2001-144900), or to provide two light sources with different emission colors and block off the light from one light source when a specific color information is unnecessary (Jpn. Pat. Appln. KOKAI Publication No. 8-314117).